1. Field of the Invention
This invention relates to air cleaners, and particularly to two-stage air cleaners having a cyclonic first-stage air separator and a second-stage filtering element.
2. Description of the Prior Art
Two-stage air cleaners are commonly used to clean air used in combustion engines and for other purposes. The air cleaner typically includes a first stage in which dirt is removed from the air by centrifugal force by rotating the air in a cyclone. The air cleaner also includes a second stage in the form of a filter element to remove dirt not separated by the cyclone.
The dirt removed by the cyclone accumulates in a separate location or chamber in the air cleaner. If the air cleaner becomes filled with dirt, it will no longer function, so some provision must be made for the periodic removal of dirt collected in the air cleaner. Typically, this is accomplished using a removable end cap or some other access to the dirt collection chamber. The provision of an effective access is difficult and adds to the cost of the cleaner. In addition, the access must be sealed to the air cleaner housing, and these seals may be subject to leakage as they wear or become misaligned. Furthermore, the provision of such an access provides no assurance that the air cleaner will be properly maintained and that the dirt collection chamber will be regularly emptied. To avoid the necessity of periodically emptying the air cleaner, some air cleaners are provided with automatic dirt unloaders. The automatic dirt unloader is essentially a one-way valve which allows dirt to exit the collection chamber but prevents air from being sucked into the chamber. However, the automatic dirt unloader must be inspected periodically to make sure that it is working properly. Even in the best of circumstances the valve usually leaks to some degree, allowing air to back flow into the collection chamber and dispersing dirt into the air cleaner.
To avoid dirt removal as well as the replacement of filter elements, disposable air cleaners have been developed. An example of a disposable air cleaner is shown in U.S. Pat. No. 4,350,509, issued to Alseth et al. This air cleaner provides an air cleaner made of lightweight, inexpensive and disposable materials, but it has limited capacity for holding dirt. In one embodiment, the air cleaner in U.S. Pat. No. 4,350,509 has a dirt collection chamber within an end cap, but the end cap is removable. The removable end cap allows the user to clean the collection chamber, but it is also subject to all of the problems of removable access doors of the prior art.